1. Field of the invention
The present invention relates no a suspension polymerization method, which is an improved method for producing polymerized particles suitable for use in the particles technology, such as space-retention agents, lubricity providing agents, functional carriers, mono-disperse particles having surface activity, standardization particles, toners, and functional fillers for providing fluidity and/or polishing properties to a paint base. The present invention pertains especially to a method for producing polymerized particles having a cavity structure containing plural cavities in the particle interior by a suspension polymerization method. The present invention also relates to a polymerized particles having a cavity structure containing plural cavities.
2. Prior Art
Heretofore, the above-mentioned polymerized particles, utilized in the particles technology for their particle functionalities, have been mainly produced by an emulsion polymerization method or a dispersion polymerization method.
The emulsion polymerization method has drawbacks as follows: (1) It is difficult to remove non-negletable impurities such as an emulsifying agent and the like; and (2) It is difficult to obtain particle sizes of 1 .mu.m or larger. The dispersion polymerization method has disadvantages such that: (1) production of the polymerized particles is an extremely costly process; and (2) mass production is inadequate because of the complexities of the method.
In order to solve the problems in the emulsion polymerization method and dispersion polymerization method described above, the present inventors have proposed a suspension polymerization method for producing a polymer powder of uniform polymer particles and the desired particle size, as disclosed in Japanese Patent Application First Publication Nos. 3-43,402 and 3-56,501. The proposed suspension polymerization method comprises the steps of:
(a) placing a dispersed phase component of a monomer composition and a continuous phase component of an aqueous medium, respectively, in two separate vessels; (b) supplying continuously and simultaneously each of the dispersed phase component and the continuous phase component in the individual vessels via the individual paths to a shearing device; (c) exerting a shear force on the dispersed phase component and the continuous component to form a dispersed material having liquid-drops of the desired size; and (d) subjecting the dispersed material to a polymerization reaction in a polymerization vessel to form a polymerized particle.
Recently, it has been desirable for polymerized particles formed using the suspension polymerization method to possess a high functionality. For example, in toner particles for electrophotocopier, the fluidity and triboelectric charging properties of the toner depend on the shape of the toner particles. Simply supplying spherical toner particles does not always ensure that all of the desired properties will be provided to the toner. Therefore, a need is to produce polymerized particles possessing improved functionalities by virtue of the specific particle shape such as an irregular shape, an internal cavity structure, or the like.
However, the interior structure of the uniformly spherical polymerized particles produced by the conventional suspension polymerization method as shown in Japanese Patent Application First Publication Nos. 3-43,402 and 3-56,501 is composed of a monomer composition as a main ingredient, and the conventional suspension polymerization method cannot provide a polymerized particle having miscellaneous shapes and a cavity structure in the particle.